The present invention relates to methods and apparatus for automatic adjustment of processing systems to achieve improvement in the apparent quality of television pictures subjected to degradation from passage through a distorting medium, such as a limited bandwidth video recorder. More particularly, the present invention relates to a method and apparatus for providing a pilot burst standard in the picture signal before degradation which, when recovered, is used for automatic adjustment of subsequent electronic enhancement processing of the signal.
Electronic enhancement techniques and systems for improving the subjective quality of television images are known. The need for enhancement has arisen particularly within the environment of industrial grade three-quarter inch video tape recorders of the helical scanning head variety. Those recorders are characterized by a limited bandwidth of about 2.5 M.Hz and are further characterized by a "coring" effect in the reproduced images. "Coring" means that the reproduced image has a cartoon-like appearance of large image outlines with washed out fine picture details. This phenomenon occurs within inexpensive video recorders because they provide even less bandwidth, not much over 1 MHz, for small level picture detail transitions, such as those on the order of 10 IRE units or less.
The present inventor has been active in the area of developing non-linear enhancement systems for television signals which have become degraded in processing, particularly video recording with industrial grade and consumer grade tape and cassette recorders. Apparatus and methods for video crispening by shortening video transition times are disclosed in the present inventor's U.S. Pat. No. 4,030,121. Noise reduction techniques are set forth in the present inventor's U.S. Pat. No. 4,121,211. Methods and apparatus for separation of chrominance and luminance with adaptive comb filtering techniques in a quadrature modulated color television system are described in the present inventor's U.S. Pat. No. 4,179,705 and in his co-pending U.S. patent application, Ser. No. 06/068,215, filed Aug. 20, 1979, now U.S. Pat. No. 4,240,105. A low level transition signal booster for television is described in the present inventor's U.S. patent application Ser. No. 06/057,701, filed July 16, 1979, now U.S. Pat. No. 4,262,304. The methods and systems described in these patents have worked excellently, providing however, that the operator has properly made adjustments required in order to bring about enhancement and improvement in subjective picture image quality.
A problem has arisen with the foregoing image enhancement techniques in that each requires a number of settings and adjustments in order to achieve enhancement that truly improves subjective image appearance. When the above systems are combined into a single overall enhancement system, the number of manual adjustments becomes large, and operator subjectivity and bias and consequent errors tend to nullify the capabilities of the enhancement systems to improve and enhance image quality. Typically, studio technicians have "painted" television images by making manual adjustments. Some technicians have been lacking in artistic ability. Others have been hampered by poorly operating or aligned color monitors. Ambient lighting and environmental color concentrations have detracted in the manual adjustment of enhancement processes.
Consequently, a need has arisen to provide an objective measurement of a subjectively balanced picture. The present inventor has discovered that a good model of subjectively pleasing fine picture details is provided in a minus 20 DB 2T sine square test pulse at 100% amplitude. If the test pulse is over 100% amplitude the image will have an excess of detail, while if under 100%, the picture will be lacking in detail. The present inventor has also discovered that a 1.7 MHz pilot test signal burst, preferably located in and occupying otherwise unused portions of the television signal, such as e.g., lines 10 to 16 on the back porch of the vertical sync pulse interval, provides an excellent emulation of the desired sine square pulse and provides an objective standard upon which to base and to adjust automatically the subjective enhancement and balancing of fine picture details in a television system subject to degradation in e.g. reduced bandwidth video recording.